[71.07] Albedo of Objects Populating the Kuiper Belt

L. Marochnik (CSC)

Method is proposed for measuring the albedo of bodies populating the Kuiper
belt (KB). This albedo likely refers to a primordial substance of the
solar system because the KB population was not exposed to significant
thermal and gravitational evolution over the lifetime of the solar system.
Knowing the albedo of KB bodies, one can estimate the actual sizes of
objects which have been observed in recent years by ground-based optical
telescopes.

The albedo can be directly measured by the location of the maximum of
the KB infrared spectrum, L. The wavelengh of this maximum depends only on
the width of the KB D and on the spatial distribution of its constituent
objects (the surface density of KB objects is assumed to vary as R^-a
where R is the heliocentric distance). However, L is largely insensitive
to both the a and D parameters over reasonable ranges ( a=2-4,
maxR=100-600 AU and minR =50 AU). Therefore, the maximum position should
determine the albedo practically independently of model parameters. One
could expect to find the maximum of the KB infrared spectrum in the
wavelength ranges 67-69 microns and 90-92 microns, e.g., for the albedos
A=0.04 and A=0.7, respectively.

The expected infrared brightness of the KB would be about
2.7x10^-13 Watt/cm^2/sr ( at its maximum) if the average Bond
albedo of its members is A=0.04 (which is close to that of short-period
comets) and about 0.84x10^-13 Watt/cm^2/sr for A=0.7 (as accepted
for long-period and new comets) if its total mass M is about 1Mearth and
the minimum size of its objects is about 0.3 km. If so, one would expect
the contrast between the KB brightness and that of the infrared background
due to galaxies and zodiacal light ( estimated at 5x10^-12
Watt/cm^2/sr ) to be 5.6%-1.7%. While this is beyond the COBE
sensitivity limit, it could be detectable by next-generation IR telescopes
(SIRTF).